For example, about 20% or more of the coal ash produced by a boiler of a coal-fired power plant, etc. is unburned carbon. Separating and collecting this unburned carbon and using it as energy source have been studied, and various proposals have been presented.
For example, WO 2002/076620 (Patent Document 1) describes an electrostatic separation method, electrostatic separation device and manufacturing system for particles, and proposes an electrostatic separation device which separates a particulate material that is a mixture of electrically-conductive components and insulating components into the electrically-conductive components and the insulating components by the electrostatic force.
FIG. 5 of Patent Document 1 (see FIG. 1 of the present application) shows one example of a conventional electrostatic separation device. This conventional electrostatic separation device is configured such that electrodes are disposed on an upper side and a lower side, a gas diffusion plate electrode (laminated sintering porous electrode) having air permeability is disposed as a lower side electrode 1, and a wind box 6 disposed below the lower side electrode 1 blows air to fluidize powder.
As an upper side electrode 2, a substantially flat plate mesh electrode having a large number of openings through which particles pass is disposed. Further, a vibrator or a knocker 5 is attached to give vibration to the entire device. Patent Document 1 describes a method for applying a DC high voltage between the upper and lower side electrodes, supplying to an electrostatic separation zone 3 the particulate material (concentration of unburned components=electrically-conductive particle weight ratio of 2% to 5%) that is a mixture of electrically-conductive particles (unburned components) and insulating particles (ash components), and carrying out the electrostatic separation while applying vibration to the device.
However, in accordance with the method described in Patent Document 1, there is a problem that in a case where the concentration of the unburned component of the particulate material that is the mixture of the electrically-conductive component and the insulating component is as high as 15% to 30%, the increase of the concentration of the electrically-conductive component in the air in the electrostatic separation zone 3 is unavoidable, and the separation performance deteriorates due to the decrease of the insulation property and the generation of the spark.    Patent Document 1: WO 2002/076620